PESHAWAR, Pakistan — Militants beheaded three members of an anti-Taliban militia in northwestern Pakistan and kidnapped three others, a government official said Tuesday.

Dozens of militants took part in the attack Monday in the Khyber tribal area, said Iqbal Khan, a government administrator in the nearby city of Peshawar. Authorities are investigating which militant group was involved in the attack, which took place in the Bara area of Khyber, said Khan.